Packet data session setup based on Offer and Answer procedures using Session Description Protocol (SDP) is used to exchange multimedia terminal capabilities and agree on a common capability before initiating a session. The Session Initiation Protocol (SIP) describes application level signaling that can carry SDP to setup a session, modify session and terminate session. The use of these protocols to setup a communication session in a packet core network utilizes the resource reservation procedures in order to efficiently make use of the radio resources to transport the media to provide the real time services. One method, defined in the 3GPP IP Multimedia Subsystem (IMS) specifications (23.228 and 24.229) has adopted the use of these IETF standards for hosting multimedia services on SIP packet core networks for mobile environments. Quality of Service (QoS) Precondition is a constraint imposed by the originating mobile to the remote end that requires reservation of resources (e.g. a secondary bearer) at both access networks while setting up the session. Before the terminating mobile alerts to an incoming call, a resource reservation based precondition shall have to be met. An originating mobile may or may not require QoS precondition to the terminating end. The terminating end may or may not support the QoS precondition.
Originating mobiles indicate the requirements for QoS precondition while setting up a SIP session based on service requirements. The originating mobile identifies the ability of the terminating mobile to support the precondition during negotiation. With this solution however, the originating mobile always begins by requiring in the SIP INVITE that the originating network and the terminating mobile support the QoS Precondition. If either does not support the QoS precondition, the originating mobile modifies the SIP INVITE based on current support, either at the originating access network or at the remote mobile, during the SIP negotiation. Modification of the procedure requires additional signaling, additional time and as a result, this diminishes the user experience.
Additionally because the mobile may roam between an IMS core network based on a 3GPP Release 5 network, a 3GPP Release 6 network, WLAN networks or the like, SIP negotiation will differ as WLAN networks do not support resource reservation management while IMS core networks do. Even further, in Release 5 resource reservation is mandatory while in release 6 resource reservation is optional.
The 3GPP IMS specification 24.229 Release 5 mandates the support for “QoS Precondition” on the Gm interface. A mobile initiated or terminated session will fail if the precondition tag is not specified in the SIP INVITE. With this model however, the SIP session initiation without the precondition would not succeed.
A 3GPP Release 6 network requires a UE to perform a detailed criteria based on service based configuration settings to identify whether a specific service would need the QoS precondition before setting up a SIP session. The criterion would be tested (i.e. required at first) at both originating and terminating mobiles during a SIP negotiation phase. This solution however may result in a mismatch between the network support for the QoS precondition and the UE requirement for precondition (either local or remote) and result in poor quality of service and even call failure in some cases. For example, when both UEs are in IMS networks they should be able to support a service with real time QoS. If the static configuration at both UEs indicates precondition not required however, then the UEs will end up in using the interactive primary bearer for media transport also.
Still Further, the UE may require the precondition for a given service, but the originating network may not enforce serve based local policy (SBLP) (Release 6 networks) but the UE shall need to know before following alternative call flows as supported in release 6.
Therefore there is a need to Shorten the SIP session setup time (i.e. reduced call setup time) and minimize number of SIP messages exchanged thereby providing a better user experience while setting up an IMS session.
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